1. Field of the Invention
The present invention relates to a measuring device which precisely measures the difference in volume between a complex shaped combustion chamber and a standard vessel in a dry state by means of cyclic pressure variation of gas in a manufacturing process of an engine.
2. Description of the Prior Art
The volume of an engine combustion chamber for a vehicle or the like needs to be controlled because it affects the engine performance or the knocking properties. However, since the engine combustion chamber has a complex shape in which valves, ignition plug, or the like are projected, it is very difficult to calculate the volume by measuring the size.
In a manufacturing process of an engine, an engine head block in which a combustion chamber is installed is transferred by a belt conveyer in a state where the combustion chamber faces upward by turning the engine head block. In order to measure the volume of the combustion chamber in this state, a method has been conventionally employed in which a transparent acrylic plate or the like having a small hole in the center is placed on the top of the combustion chamber, liquid is dropped from a buret to the hole until the combustion chamber is filled with the liquid, and the volume of the combustion chamber is obtained by measuring the volume of the dropped liquid. However, this method has drawbacks, for example, in that it needs a long period of time and also the liquid has to be removed after the measurement.
On the other hand, as a method for measuring the volume of a complex shaped object in a dry state, there has been known a method in which the object is placed in a container, cyclic volume variation is produced in the internal space of the container by using a sound source such as a speaker so as to adiabatically compress and expand gas within the container, and the volume of the object is obtained from the magnitude of cyclic pressure variation irrespective of the shape of the object.
As a measuring instrument of this type, Parker (U.S. Pat. No. 4,474,061 (1984)) discloses a device which measures the amount of fuel in a tank. In Japanese Pre-grant Patent Publication No. 2-33,084 (1990), the inventor of the present application has proposed an acoustic volumeter which differentially produces cyclic volume variation in both a reference chamber and a measuring chamber, and measures the volume of the free space within the measuring container based on the ratio of the magnitude of gas pressure variation between these chambers, i.e. the ratio of the magnitude of sound pressure generated at that time, so as to obtain the volume of an object placed within the measuring chamber. Pond (U.S. Pat. No. 4,561,298 (1985)) discloses a device that measures the volume of the free space within a container using a similar method. Further, in Japanese Patent Application Publication No. 5-223,616 (1993), the inventor of the present application has proposed an acoustic volumeter which is not influenced by changes in the constituents of gas such as humidity in the air by means of an equalizing pipe provided between the reference chamber and the measuring chamber. Dempster (U.S. Pat. No. 5,105,825 (1992)) discloses a device which measures the volume of a human body by using an acoustical method, calculates the density of the human body from the measured volume and the weight of the human body, and then obtains the percent of body fat. The object of these inventions is to measure the volume of fuel or an object placed in a container. In contrast, the object of the present invention is to measure the volume of a container itself, i.e., an engine combustion chamber.
In Japanese Patent Application Publication No. 8-29232 (1996) which has been issued as Japanese Patent No. 3,525,502 (2004), the inventor of the present application has proposed an acoustic volumeter which measures the total volume of an engine combustion chamber and a cylinder by feeding sound thereinto through a connecting pipe coupled to a plug hole of an assembled engine. Since the volume is directly measured from the magnitude of the sound pressure and the influence of the acoustic impedance of the connecting pipe is included in this device different from the present invention, the measuring equation of this device is totally different from that of the present invention which measures volume difference between the combustion chamber and the standard vessel.
In U.S. Pat. No. 5,824,892 (1998), the inventor of the present invention has proposed an acoustic volumeter in which cyclic volume variation is differentially produced in a reference container and a measuring container by using a speaker, and the ratio of the magnitude of sound pressure between these containers are detected, so as to measure the volume difference between an object placed in the measuring container such as a precision weight and a standard object to be compared. This invention is referred to as the conventional invention hereinafter.
In the conventional invention, if the volume of the standard object to be compared is known, the volume of the object to be measured can be known by adding the measured volume difference to the volume of the standard object. However, in the case of a combustion chamber, the volume of the chamber itself is to be measured rather than the volume of an object placed therein. Therefore, in order to use the magnitude of sound pressure as shown in the conventional invention, since the conventional invention cannot be directly applied, it is necessary to introduce a new device which has a different structure and measuring method from the conventional invention.